Abstract NIMH Research domain criteria (RDoC) are a guiding framework for etiologic research in psychopathology. The RDoC Social Communication (SC) construct represents an important component of several forms of developmental psychopathology, including autism spectrum disorder (ASD). A key next step in the application of RDoC SC criteria toward understanding developmental psychopathology will be to identify, differentiate, and measure SC sub-constructs. The over-arching long-term goal of this application is to develop brief, quantitative, subjective parent report and clinician observation measures of RDoC SC sub- constructs relevant to developmental psychopathology. To achieve this goal, we will first empirically identify and differentiate broad and specific RDoC-relevant SC sub-constructs using de-identified clinical and behavioral data from samples an order of magnitude larger than all previous studies (Aim 1). This approach will identify a generalizable structure of SC behavior by combining data across datasets and applying advanced statistical methods that simultaneously extract SC dimensions from multiple measures and information sources (parent report, parent interview, and clinician observation). Next, using the results of aim 1 and an exhaustive review of the social communication literature, we will fill in the SC map by conducting additional quantitative and qualitative analyses focused on identifying SC facets that were not adequately represented by existing item sets (Aim 2). Finally, using the results of Aims 1 and 2, we will develop and pilot test parent report and clinician observation measures of RDoC-relevant SC sub- constructs. To accomplish these aims, the proposed project will analyze data from eight large-sample sources that include measures of social behavior on more than 30,000 children (ages 2-18) with a range of social communication abilities - from severe ASD to other psychiatric disorders to healthy controls. After SC sub-structure is identified, we will write parent-report and clinician observation measures and pilot test these measures for content validity, readability, and parent acceptability. If the above aims are achieved, the proposed project will represent a critical first step toward the development and dissemination of RDoC- relevant SC measures that can linked to other RDoC levels of analysis (genetic, cellular, neural systems, etc.), applied in future research to improve our understanding of developmental psychopathology, and implemented in clinical practice to enhance patient care.